Ribbon microphones are known for their sort of warm natural sonics. They have really desirable characteristics especially for things like vocals. And, what they do, they consist of a ribbon which is a very, very thin corrugated sheet of aluminum that is suspended in a magnetic field. Incoming sound waves cause the ribbon to vibrate, moving conductor in a magnetic field will generate a voltage across the conductor and be an indicator of the sound field. So there are a number of manufacturers, probably the most famous initial group of microphones is made by RCA.
FIGS. 1A and 1B illustrate a couple of conventional ribbon microphones. These are a couple of classics by RCA. Personnel at RCA invented the ribbon microphone. The RCA-44 is shown—labeled 1101 and the RCA-77 is labeled 1102. Also shown is a figure from one of their early patents, that shows a think corrugated strip of aluminum labeled 1105 suspended in a magnetic field created by the magnet 1104. So, sound impinging on this strip will cause it to vibrate. It's conductive. A moving conductor in a magnetic field will develop a voltage across its terminals and this voltage will represent the sound field and that's the voltage that gets sent to a delay transformer and then on to a preamp and then onto whatever the recording engineers wants to do with it.
So, these ribbon microphones are really quite desirable for a number of applications. People use them for vocals, they use them for horns and the like. They have a natural warm sound that is desirable. They have also a strong polar pattern. As can be appreciated, the ribbon will move in response to pressure difference between the front of the ribbon and the back of the ribbon and therefore sound arriving from the side of the ribbon will not produce an output whereas sound coming from the front or back will produce a relatively loud output.
FIG. 1B shows a detail of a ribbon microphone, in which a couple of magnets 1106, have a ribbon, this thin corrugated strip of aluminum 1107 suspended between them. Presumably the south pole of one of the bar magnets is opposite the north pole of the other. So, these ribbon microphones are very delicate, mechanically and acoustically. The ribbons are very thin and really designed such that if their molecules are moving back and forth, the ribbon is just going to move back and forth with them. They are suspended with very little tension. In fact, if one were to tilt a ribbon microphone onto its side, if one could take off the various wind screens etc., one would see that that the ribbon will sort of sag under force of gravity. If one were to blow on a ribbon microphone it would break. Some repairs to the ribbon, if that were possible, would be needed. However, if one wanted to have a working microphone, a new ribbon would more likely be needed. So, this sensitivity to acoustics, as well as the mechanical sensitivity inherent in these microphones, does limit their use. They are not likely to be used on a kick drum for instance. However, they do get used for vocals and horns and the like. They probably are not going to be used in a lodge setting. So, they have a few drawbacks in terms of their mechanical and acoustic robustness, so they also have low output levels and these things limit their usage.
The housings in the microphones shown in FIG. 1A are designed such that the polar pattern has been changed into a cartoid pattern. Once nice thing about ribbon microphones is that they have a very strong polar pattern. Differential sound pressure front to back will cause the ribbon to be moved in that transverse direction so that sounds coming from the front or back will displace the ribbon where a sound is coming from the side present no differential pressure to the ribbon and it is not displaced. So you have null coming out the sides which can be used to put a couple horn players in front of a couple of ribbon microphones and have one horn player placed in the null of the other horn player's microphone and vice versa.
The issues with conventional ribbon microphones include that they are very delicate, mechanically and acoustically. If one were to blow onto the ribbon it would deform and it would not be able to be put back to its original shape. They definitely cannot be dropped without being damaged. Also, their output levels are not up to standard. So, there are some businesses that manufacture these microphones today but they are expensive, and they are not very mechanically and acoustically robust, so they are not the kind of thing that an unsophisticated user could handle and they are not the kind of thing useful for drums or instruments that are super loud. They are not suited to being used for live performances. There are limited places that they can be used even though they have a desirable sound.
FIGS. 5A and 5B show a photograph and a couple of mechanical drawings of microphones from Beyerdynamic, respectively. In FIG. 5B, there is a 1930 vintage ribbon microphone showing a corrugated aluminum strip 1201 suspended in a magnetic field created by magnet 1202. The corrugations on this microphone are generally perpendicular to its axis. There are a couple of microphones 1203 and 1204 that have corrugations going between the points that the ribbon is suspended. The photograph in FIG. 5A shows the ribbon inside a housing and 1205 would likely be the mounting for the housing of the ribbon and 1206 shows the actual ribbon. This ribbon has a couple corrugations that are perpendicular to its length and then several corrugations that are along its length. The idea is that the corrugations will make the microphone stiff on that one axis. This microphone was put in a housing that would create a time delay between signals arriving from the back and arriving from the front and as a result of that the polar pattern for this particular microphone is not a classic figure of eight, it's more of a cartoid pattern.
A BBC engineering monograph by D. E. L. Shorter and H. D. Hardwood entitled “The Design of a Ribbon Type Pressure-Gradient Microphone for Broadcast Transmission” (1955) describes a number of technical aspects of the ribbon microphones in terms of anything from their frequency response to various mechanical details, as well as images of the insides of several microphones showing their construction.